A conventional example of the methods for efficiently freeze-drying a liquid material to be dried such as an aqueous solution of pharmaceutical includes a method of supplying the material to be dried onto an inner circumferential surface of a vertical tube and freezing the dried material, and freeze-drying the frozen dried material under reduced pressure (for example, see Patent Document 1).
The conventional technique includes a vertical tube, liquid-supply means for supplying a liquid material to be dried to spray means provided at an upper portion of the vertical tube, a liquid-recovery passage connected to a lower portion of the vertical tube so as to recover excessive dried material, and freezing means arranged around the vertical tube so as to control a temperature of an inner circumferential surface of the vertical tube.
The liquid dried material supplied from the liquid-supply means is sprinkled and supplied onto the inner circumferential surface of the vertical tube by the spray means. The inner circumferential surface of the vertical tube is formed with a frozen surface which is cooled by the freezing means to thereby freeze the dried material onto the frozen surface into a shape of a pipe. At this time, the excessive dried material that has flowed down to the lower portion of the vertical tube is recovered to the liquid-supply means via the liquid-recovery passage. When a predetermined amount of the dried material has been supplied, the supply of the dried material from the liquid-supply means is stopped, and the pressure within the vertical tube is reduced. Then the freezing means is switched to heating means by increasing its cooling medium temperature, and the heating means adds sublimation heat to the frozen dried material, thereby enabling the frozen dried material to be freeze-dried.
The vertical tube has a lower end portion, to which a flange with a nozzle is assembled. The flange incorporates a jet nozzle. If the dried material within the vertical tube is freeze-dried into the shape of a pipe, the dried material is scraped off from the frozen surface, received by the flange with a nozzle, and roughly crushed by air injected out of the jet nozzle. The roughly crushed dried material is transported by the air to a jet mill to be crushed into a more fine powder state. Thereafter, a cyclone device captures and collects the fine powder, which is recovered into a bulk can or the like.
Patent Document 1: Japanese Patent Laid-open Publication No. 2004-330130